Can’t access localhost files

Pressing that button means you enabled the web server, so your Mac is (now) a web server.

Great work! :)

Good to hear, your welcome. :)

Shelley the stock untouched Hosts File...

##

# Host Database

#

# localhost is used to configure the loopback interface

# when the system is booting. Do not change this entry.

##

127.0.0.1 localhost

255.255.255.255 broadcasthost

::1 localhost

fe80::1%lo0 localhost

In support of MrHoffman's statement above:

The underlying concept is that the box they provide has two devices inside: one provides a Switch function, based on settings, that sends packets intended for local use directly to local devices without Routing. The simplest example of this is packets for your local Network printer, which would have a similar, but not identical IP address to your computer.

The second is the better-know Router function, where packets that OBVIOUSLY are intend for the Internet are presented to the Internet 'on your behalf'. These packets are inspected and their source is changed so that they appear to her come from your Router (using a technique called Network Address Translation). Suffice it to say this process is sufficiently complex that local packets should never be leaving your local Network, but should be SWITCHED along to other devices on your local Network only.